Thermal powered VAV ceiling diffusers are widely used in HVAC systems to control the temperature within an occupied space. The VAV ceiling diffuser is connected to a heating and cooling duct of the HVAC system. The heating and cooling duct supplies either warm or cool air to the diffuser. The diffuser has thermal sensors/actuators that sense the temperature of the air supplied in the duct and the temperature of the occupied space. Based on the sensed temperatures, the thermal sensors/actuators drive a linkage that opens and closes a damper to increase or decrease the amount of heating or cooling air supplied to the occupied space in order to maintain a relatively constant temperature in the occupied space.
The prior art discloses a number of thermal powered VAV ceiling diffusers that employ various linkages for controlling the movement of the damper in response to the duct temperature and the room temperature. Because the sensors/actuators provide limited movement, the linkages must be able to translate that limited movement into accurate positioning for the damper in order to control the temperature in the occupied space.